Tap changer switch with radial pressurized movable contact structure

ABSTRACT

A tap changer switch for mounting within the casing of an electrical transformer, and operable from outside the casing. An insulating base member carries a plurality of stationary contacts, adapted for connection to the transformer winding, and a shaft member is disposed through an opening in the insulating base member such that it extends outwardly from both sides thereof. One outwardly extending portion of the shaft member carries a movable contact assembly which selectively shorts two adjacent stationary contacts, and the other outwardly extending portion of the shaft member is adapted to extend through the wall of the casing of the associated transformer, and it includes a handle for rotating the shaft and selecting the two stationary contacts to be shorted.

United States Patent Ristuccia [451 Mar. 28, 1972 [72] Inventor: DonaldJ. Rlstuccia, Athens, Ga.

[73] Assignee: Westinghouse Electric Company, Pittsburgh, Pa.

[22] Filed: Sept. 28, 1970 [21] Appl. No.: 75,916

[52] US. Cl. ..200/8 R, 200/11 TC, 200/166 BB [51] ..H0lh 19/56 [58]Field of Search ..200/8 R, 11 TC, 166 BB [56] References Cited UNITEDSTATES PATENTS 2,903,530 9/1959 Wilson, Jr. ..200/8 R X 1,285,78611/1918 Nies ..200/8 R 1,412,002 4/1922 Hendricks, Jr ..200/8 R1,458,484 6/1923 Habicht ..200/8 R X 1,725,078 8/1929 Hill ..200/8 R1,785,575 12/1930 Blume ..200/8 R 3,170,048 2/1965 Glatz et al......200/11 TC 3,467,794 9/1969 Ristuccia ..200/11 TC Primary Examiner-J.R, Scott AttorneyA. T. Stratton, F. E. Brouder and D. R. Lackey [5 7]ABSTRACT A tap changer switch for mounting within the casing of anelectrical transformer, and operable from outside the casing. Aninsulating base member carries a plurality of stationary contacts,adapted for connection to the transformer winding, and a shaft member isdisposed through an opening in the insulating base member such that itextends outwardly from both sides thereof. One outwardly extendingportion of the shaft member carries a movable contact assembly whichselectively shorts two adjacent stationary contacts, and the otheroutwardly extending portion of the shaft member is adapted to extendthrough the wall of the casing of the associated transformer, and itincludes a handle for rotating the shaft and selecting the twostationary contacts to be shorted.

10 Claims, 7 Drawing Figures BACKGROUND OF THE INVENTION 1. Field of theInvention The invention relates in general to tap changers forelectrical transformers, and more specifically to tap changers adapted.for mounting within the casing of a transformer and operable fromoutside the casing.

Description of the Prior Art US. Pat. No. 3,467,794, which is assignedto the same assignee as the present application, discloses a tap changerswitch of the type which is mounted wholly within the casing of anelectrical distribution type transformer, and connected to a pluralityof taps on the high voltage winding thereof. The desired tap position isselected by the electrical utility at the time of installing thetransformer, as required by the specific operating location within theelectrical distribution system. If the conditions change at some time inthe future, requiring a higher or lower tap setting to provide thedesired output voltage, the tap changer switch may be set to the desirednew operating position. However, since the tap changer switch is mountedwholly within the casing, the transformer cover, or the cover of asealed hand-hole opening in the cover, must be removed to permit accessto the operating handle of the tap changer switch. While the frequencyof required tap changes during the normal service life of a distributiontransformer is very low, it would be desirable to be able to operate thetap changer without breaking the transformer seal. In addition to beingtime consuming and, therefore, costly, each time the transformer seal isbroken opportunities are present for contaminating the mineral oil,which may shorten the useful operating life of the transformer.

The tap changer switch disclosed in the hereinbefore mentioned US. Pat.substantially reduced the manufacturing cost of the tap changer,compared with certain tap changers of the prior art, and it wouldtherefore be desirable to utilize the basic switching mechanism of thistap changer for an externally operable tap changer switch. However,extending the 'length of the operating handle of this switch through asealed opening in the casing of the distribution transformer presentsboth space and functional problems. The movable contact of the switchmechanism is at an elevated potential, i.e., such as about 50 percent ofthe line potential, and therefore the handle must be extended to providethe required clearance between the movable contact and the wall of thecasing. The length of the required shaft extension is such that theswitch requires a substantially larger space within the transformer,interfering with the space and electrical clearances required by thesecondary circuit breaker, as well as other apparatus mounted in the oilabove the transformer, such as protective fuse links. Thus, changing theorientation of the switch operating shaft from vertical to horizontaland bringing the shaft through the side wall of the casing to make itexternally operable, presents problems in obtaining the desiredinsulating clearances, and may require a larger tank size than would .berequired by a similar switch wholly mounted within the casing.Maintaining the switch in its prior art vertical position and ,extendingthe shaft through a sealed opening in the cover of the transformerisalso undesirable, as not only would a long.

operating shaft be required in order to keep the switch operat-. ingmechanism below the oil level, it would present assembly problems.Longtap leads would have to be connected to the.

switch if the switch were to be mounted on the cover, which would createmechanical and electrical problems whenthe cover is mounted on the tank.The switch would also be more difficult for the lineman to actuate.

An unduly long operating shaft on the tap changer switch may presentfunctional problems, as at least theportion of the shaft'to which themovable contact member is fixed must be formed of an insulatingmaterial, such as wood or a synthetic resin material, which may warp,bend or twist if supported only at its extreme inner end and at the tankwall, and actu- SUMMARY OF THE INVENTION "Briefly, the present inventionis a new and improved tap changer switch adapted for mounting within thecasing of an electrical distribution transformer, and operable fromoutside the casing, which enables the relatively low cost but reliablecontact mechanism disclosed in U.S. Pat. No. 3,467,794 to be utilizedwithout requiring the useof an unduly longoperating shaft which wouldpresent the space and support problems hereinbeforedescribed.Specifically, the new and improved tap changer switch includes aninsulating base member having first and second ends or sides, an openingwhich extends between its sides, and a plurality of stationary contactmembers which extend outwardly from its first side in spaced,circumferential relation about the opening. A shaft member having firstand second ends is disposed through the opening, rotatably supported bybearing means associated with the insulating base member, such that theshaft issupported near its midpoint, with the first end of the shaftextending outwardly past the first side of the insulating'base member,and past the ends of the outwardly extending stationary contacts, andthe second end of the shaft extending outwardly past the second side ofthe insulating base member, and through an opening in a mounting hub,which is sealingly mounted through an opening in the transformer casing.The shaft extends through the mounting hub for a sufficient distance toenable an operating handle to be fixed to this end of the shaft, whichis outside the casing. The insulating base member is thus disposedbetween the movable contact and outwardly extending stationaryco'ntacts, and the casing, enabling the insulating base and contactstructure to be mounted close to the. wall of the tank or casing. Theoperating shaft, being supported near its midpoint, and also at the wallof the casing by its mounting hub, ensures that it will not warp, bendor twist to the point where it would hinder or prevent operation of thetap changer at some future date.

BRIEF DESCRIPTION OF THE DRAWING FIG. 3 is an end-view of the tapchanger switch FIG. 2,as viewed from outside the casing ofthe'dis'tribu'tion transformer;

FIG. 4 is a side elevational view, partially in section ora ap changerswitch constructed according to 'aIiotlferernbodiment of the invention;I

FIGJS is an exploded perspective view Iof the movable contact structureof the tap'changer switchshdwn inFIG. 4;? FIG. 6 is a fragmentarysectional'elevationof a tap cha n ger switch constructed accordingtoanother 'embodIment of the invention; and

FIG. 7 is an exploded perspective view of the "mdvable'bon tactstructure of the tap changer switch s'hown in'FlG. 6.

DESCRIPTION or PREFERRED: EMBODIMENTS Referring now to the drawings, FIG'. 1 is a partialiy exploded perspective view of a tap changer switch10 constructedac cording'to the teachings of the'inventiomand' FIGS. 2and 3 are side and end elevational views, respectively, of tap changerswitch 10 shown mounted through the side wall por tion 12 of anelectrical distribution transformer. The operating mechanism 11 of tapchanger switch is disposed below the oil level 14 of the transformer,and it includes contacts, such as contacts 32 and 40, which areconnected to the high voltage winding of the transformer, such as viaelectrical leads 16 and 18, respectively.

Tap changer switch 10 includes an insulating base member 20 formed of aninsulating material compatible with the mineral oil insulating andcooling dielectric normally used in distribution transformers, such as amolded glass filled polyester material, with the insulating base member20 having first and second sides or ends 21 and 23, and a substantiallycentrally disposed hub portion 22. Hub portion 22 has first and secondends 24 and 26 located on sides 21 and 23, respectively, of theinsulating base member 20, and a main opening 28 which extends betweenits ends. Main opening 28 in hub 22 has a first inside diameter whichsteps outwardly to larger second and third inside diameters adjacent itsfirst and second ends 24 and 26, respectively, providing a shoulder orstep between the first and second inside diameters, and a shoulder orstep between the first and third inside diameters, for purposes whichwill be hereinafter explained.

Insulating base member 20 also includes a plurality of additionalopenings which extend between its first and second sides 21 and 23, forreceiving a plurality of stationary electrical contact members. Theplurality of additional openings are disposed about the main opening 28,and spaced circumferentially about an imaginary circle whose centercoincides with the axis of the main opening 28. The number of theseadditional openings depends upon the number of operating positions thetap changer 10 is to include. As illustrated in the Figures, tap changer10 has five operating positions, which requires a total of sixstationary contacts referenced 30, 32, 34, 36, 38 and 40, and thus sixopenings are required through the base member 20 for receiving thestationary contact members.

The stationary contact members 30, 32, 34, 36, 38 and 40 each have firstand second ends, such as first and second ends 42 and 44, respectively,on stationary contact member 32, with their second ends being disposedin one of the openings which encircle the main opening 28. Thestationary contact members are fixed in the openings such that theirfirst ends extend perpendicularly outward from at least the first side21 of the base member 20 for a predetermined dimension. As will behereinafterexplained, the loading on the stationary contacts will beradial, and not axial. Therefore, the stationary contacts may beconstructed of cylindrical, tubular electrically conductive material,such as copper tubing, having predetermined inside and outsidediameters. The predetermined outside diameter is selected to provide aclearance fit with the diameter of the plurality of openings in the basemember 20. The contact members are cut to length from the tubing, andthey are each flared outwardly with a suitable tool to provide acircumferential bulge or protrusion therein apredetermined dimensionfrom their second ends, such as the circumferential bulge 46 shown oncontact member 32. The stationary contact members may have their secondends inserted into the plurality of openings, starting at the first side21 of the insulating base member 20, until their circumferentialprotrusions reach the start of its associated opening in the base member20. The dimension of the circumferential protrusion near the second endof each contact member is selected such that its second end extendsoutwardly from its associated opening for a distance sufficient to allowit to be flared radially outward and provide a lip, such as lip 48 onthe second end 44 of stationary contact member 32, adjacent to theopening, to firmly secure the stationary contact members within theirassociated openings.

The opening in each of the tubular stationary electrical contact members30, 32, 34, 36, 38 and 40, facilitates the connection of the electricalleads from the transformer winding thereto. For example, as shown inFIG. 2, the electrical insulation may be stripped from the ends of thetap leads, and each may be inserted into the opening in one of thestationary contacts, starting at its second end, such as lead 16 shownentering the second end 44 of contact member 32. The wall of the tubularcontact adjacent the bared end of the lead may then be crimped orotherwise pressed inwardly, as shown at 50 on contact member 32, tofirmly grip the lead and provide an excellent electrical contact betweenthe stationary contact member and its associated electrical lead.

A metallic mounting hub 60 is provided, which may be economically diecast, such as from aluminum or brass, having first and second ends 62and 64, respectively, a mounting flange 66 disposed between its ends 62and 64, and an opening 68 which extends between its ends. A firstsubstantially cylindrical portion 70 is provided adjacent end 62, whichhas a plurality of threads 72 disposed on its outer surface, andparallel flat portions 74 and 76 are cut on opposite sides thereof,which flats aid in orienting the mounting hub with respect to theinsulating base member, as will be hereinafter explained. A secondcylindrical portion 78 is provided adjacent end 64, which has aplurality of threads 80 disposed on its outer surface. Cylindricalportion 78 steps outwardly to provide the hereinbefore mentionedmounting flange 66, forming a flat surface 82 facing end 64 of themounting hub 60, in which an annular groove is disposed for receiving agasket member 84.

Opening 68 in mounting hub 60, and opening 28 in the insulating basemember 20 are coaxially aligned, and this alignment maintained, as wellas the required circumferential orientation of the insulating basemember 20 relative to the mounting hub 60, by a bracket member which hasfirst and second spaced parallel portions 92 and 94, respectively, and aportion 96 which interconnects the spaced parallel portions 92 and 94.Portion 92 of mounting bracket 90 has spaced openings therein, intowhich nut and bolt assemblies 98 and 100 may be inserted, and alsothrough similarly spaced openings in the insulating base member 20, tofix the insulating base member to the bracket member 90. Portion 94 ofbracket member 90 has a single opening disposed therein, shaped tosnugly receive the configuration of portion 70 of mounting hub 60, withthe flat portions 74 and 76 properly orienting the mounting hub 60relative to the insulating base member 20. A nut 102 is threadablyengaged with portion 70 of mounting hub 60, after end 62 has beeninserted through the opening in portion 94 of the bracket 90, to securethe mounting hub 60 to the bracket member 90. Operating shaft means 110,having first and second ends 112 and 114, is disposed through theopening 28 in the insulating base member 20 such that the first end 112extends outwardly past the first side 21 of the insulating base member20, and past the ends of the outwardly extending stationary contactmembers, such as past the end 42 of stationary contact member 32, for asufficient distance to carry a movable contact assembly 120, which willbe hereinafter described.

Operating shaft means also extends outwardly from the second side 23 ofinsulating base member 20, for a distance sufficient to extendcompletely through the opening 68 in the mounting hub 60, and pass thesecond end 64 of the mounting hub for a sufficient dimension to permitan operating handle 130 to be fixed thereto, as will be hereinafterdescribed. Shaft means 110 has first and second portions 122 and 124, ofdifferent diameters, with portion 122 being associated with theinsulating base member 20, and with portion 124 extending through themounting hub 60. Portion 122 of shaft means 110 has two spacedcircumferential grooves 116 and 118 disposed therein, such that thegrooves are within opening 68 of mounting hub 60, with resilient gasketor O-ring members 117 and 119 being disposed in the circumferentialgrooves 116 and 1 18, to seal the opening 68 while allowing rotarymotion of the shaft means 1 10.

At least the portion 122 of shaft means 110, to which the movablecontact assembly 120 is fixed, is formed of an electrical insulatingmaterial, such as wood or a synthetic resin, such as glass filledpolyester, or a glass filled polyamide. Thus, the shaft means 110 may beof one-piece construction, being wholly formed of insulating material;or, as illustrated in FIG. 2, shaft means 110 may have portion 122formed of an insulating material, to which the movable contact assemblyis attached, and portion 124 may be formed of a metal, such as brass,with portions 122 and 124 being fixed to one another by any suitablemeans, such as by an extension 126 on portion 124 which enters anopening in the adjacent end of portion 122, and a pin 128 which entersaligned openings in both portrons.

Shaft means 110 is fixed within opening 28, in rotary relation with basemember 20, by washer members 132 and 134, respectively, and a pin member136. Washer member 134 is not essential, as handle 130 will preventaxial movement of shaft 110 in the direction into the casing, but may beused if desired. Washer member 134 is a metallic retainer type washerformed of a material such as steel, which has an inside diameter sizedto allow it to be pressed over the second end 114 of shaft means 110 tothe desired location, and to bite into the shaft and to resist anyfurther relative movement between the shaft and washer. Washer member134 has an outside diameter sized to cooperate with the surface whichdefines the third inside diameter of opening 28, adjacent end 26 of hubportion 22, to provide a radial bearing which allows the shaft means 1l0 and washer member 134 to rotate when the shaft is turned. In otherwords, the outside diameter of washer member 134 is just slightly lessthan the third inside diameter of opening 28 adjacent end 26. Washermember 134 is disposed adjacent the step formed by the first and thirdinside diameters of opening 28, with the step in washer member 134cooperating to provide a thrust bearing when an attempt is made to moveshaft 70 axially in the direction from end 23 to end 21 of theinsulating base member 20.

Washer member 132 may be a conventional metallic washer formed of steel,which has an inside diameter slightly larger than the outside diameterof portion 122 of the shaft means 110, to allow it to be easily slippedover the shaft, and an outside diameter sized to cooperate with thesurface which defines the second inside diameter of opening 28, adjacentend 24 of the hub portion 22, to provide a radial hearing which allowsshaft means 110 to rotate when the shaft is turned. The radial bearingat end 24 of hub portion 22 may initially be between the shaft means 110and the inside diameter of washer member 138, since the shaft outsidediameter is slightly smaller than the inside diameter of washer member132. However, if the outside diameter of the insulating portion 122 ofshaft means 110 swells to the point where it causes the washer member132 to be fixed to the shaft, the shaft and washer member 132 will turntogether and the radial bearing will then be between the outsidediameter of washer member 132 and the surface which defines the secondinside diameter of opening 28.

The pin member 136 is disposed through a transverse opening formed inthe shaft portion 122, immediately adjacent to washer member 132, suchthat the pin member 136 will retain washer member 132 within the secondinside diameter of opening 28. When an attempt is made to move shaft 70axially in the direction from the first end 21 to the second end 23 ofbase member 20, the pin 136 functions as a thrust bearing by contactingthe surface of base member 20 surrounding the opening 28, and thesurface of washer member 132. Any axial force placed on washer member132 will be resisted by the step formed between the second and firstinside diameters of opening 28. Therefore, the washer member 132 andadjacent step also cooperate to provide a thrust bearing.

The pin 136 extends outwardly from one side of the shaft means 110 for apredetermined dimension, which also allows it to cooperate with aprojection 140, best shown in FIG. 1, which projects outwardly from end24 of the hub portion 22, to provide a positive stop at both the lowestand highest numbered tap positions. The arcuate dimensions of projection140, and the orientation of pin member 136, are selected according tothe number of tap positions the tap changer is to have. Projection 140,in this example, is sized to allow five tap positions, with the firsttap position starting between stationary contacts 30 and 32, and thefifth tap positions being between contacts 38 and 40. The projection andpin 136 will not allow a tap changer position between stationarycontacts 30 and 40.

The movable contact assembly 120 is fastened to portion 122 of shaftmeans 110. Movable contact assembly 120, in this embodiment, includes aleaf spring 142 and a contact shoe 144. Leaf spring 142, which may beformed of a good spring material such as 18-8 stainless steel, has anobtuse bend 146 therein, forming a first straight portion 148 and asecond straight portion 150. The first straight portion 148 of the leafspring 142 is fastened to shaft portion 122, such as by screws 152, suchthat the second straight portion 150 extends outwardly from shaftportion 122 towards end 114 of the shaft means 110. Leaf spring 142 isfixed to shaft portion 122 at a location which will cause the end of thesecond straight portion 150 to be adjacent to the plurality ofstationary contacts.

Contact shoe 144 may be formed of any suitable electrical conductor. Forexample, sintered powdered copper or brass, or combinations thereof, maybe used since the contact shoe may be molded to the required shape.Contact shoe 144 is fixed to the outwardly extending end of the secondstraight portion 150 of leaf spring .142, and it is sized such that itwill extend between and contact two adjacent stationary contact members,such as contact members 30 and 32 as illustrated in FIG. 1, under apositive radial force provided by leaf spring 142. To provide thepositive detent or snap action necessary when the tap changer reaches anoperating position, as well as to wipe the contacts clean as the tapchanger is actuated to change tap positions, the contact shoe 144 shouldhave a substantially trapezoidal shape or configuration in a plane whichis substantially perpendicular to the axis of the shaft means 110. Thesmall end of the trapezoidal configuration extends between two adjacentspaced stationary contact members, and the large end of the trapezoidalconfiguration should be longer than the distance between two stationarycontacts, in order to cause the contact shoe 144 to contact thestationary contacts with its two surfaces which slope inwardly from thelarge end to the smaller end.

Since the force applied to the stationary contacts is radial, themovable contact assembly 120 should be positioned axially with respectto shaft means 110, such that the contact shoe 144 will contact thestationary contact members as close as practical to the points wherethey are secured to the base member 20, in order to insure that thestationary contacts will remain parallel with one another.

Tap changer 10, as described to this point, is now ready for mountingthrough an opening in the side wall 12 of the transformer casing. Thedesired orientation of the tap changer switch 10 may be obtained bydisposing a longitudinal groove across portion 78 of the mounting hub60, which is aligned with an oriented projection which extends into theopening in the wall 12 of the transformer casing into which the tapchanger switch is to be mounted. If the bracket member 90 is formed ofan insulating material, as illustrated in FIG. 2, tap changer switch 10may be oriented as shown in FIG. 2, relative to the oil surface 14. Ifthe bracket member 90 is formed of a metal, adequate clearance betweenthe tap leads and the bracket member 90 may be obtained by mounting thetap changer 10 such that it is rotated from the orientation shown inFIG. 2, such as shown in the embodiment of FIG. 4.

Prior to inserting end 64 of mounting hub 60 into the opening in casing12, gasket member 84 is placed in the annular groove in the face of theflange portion 66. Then, after end 64 has been inserted into the openingin the casing 12, gasket member 162 is inserted over end 64, against theoutside wall of the casing 12, and then one or more nuts, such as nut164, is threaded over portion 78 of the mounting hub 60, to firmlysecure the tap changer 10 to the casing 12.

Operating handle 130, having a blind opening 164 sized to snugly receiveend 114 of shaft means 110, and a transverse opening 166 for receiving apin 168, is then slipped on end 114 of the operating shaft means 110,with opening 166 being aligned with a similar sized opening throughportion 124 of the shaft means 110. Pin 168 is then forced into thealigned openings to secure the operating handle 130 to shaft portion124, with the handle automatically being oriented according to theoperating position of the tap changer 10. End 64 may have'numbers casttherein to identify the operating position of the switch, as shown inFIG. 3, and the tap changer operating handle 130 may be locked in thedesired operating position, preventing accidental movement of theoperating handle, by providing a blind opening in the end 64 of mountinghub 60, adjacent each operating position, such as openings 180, 182,184, 186 and 188, and a threaded opening 170 through the operatinghandle 130 for receiving a bolt 172. When it is desired to operate thetap changer, bolt 172 is backed out of the opening disposed in end 64,into which it is extending, the tap changer 10 is actuated to its newtap position, and then the bolt is advanced into the opening in end 64associated with the new tap position, preventing any further rotarymovement of the handle 130.

The hereinbefore described construction of tap changer l facilitatesassembly of its component parts. The mounting hub 60 is preparedbyattaching the bracket 90 thereto, with the nut 102. The stationarycontacts may be inserted into the openings in the insulating base member20, and then the second ends may be flared outwardly with a suitabletool, to secure them in their operating positions. The shaft means 1 mayhave the O-ring type gaskets 117 and 119 disposed in the annular grooves116 and 118, respectively, pin 136 may be disposed through thetransverse opening in the shaft means 110, and the movable contactassembly 120 may be fastened to portion 122 of the shaft means 110.Washer member 132 may be dropped into place in the base member or it maybe disposed over the second end 1 14 of the shaft means 110. The secondend 114 of shaft means 110 may then be inserted through opening 28,starting at the first end 24 of the hub portion 22. Retainer washer 134may then be forced over end 114 of shaft means 110, as the end 1 l4emerges from end 26 of the hub portion 22, and the shaft means 110advanced into and through the opening 68 in the mounting hub, until theshoulder between portions 122 and 124 of the shaft means 110 contactsthe first end 62 of the mounting hub 60. The bracket 90 may then besecured to the insulating base member 20 with the nut and boltassemblies 98 and 100, the tap changer 10 is ready for mounting in thetransformer, as hereinbefore described. Before the transformer is filledwith mineral oil, the tap leads are inserted into the openings of therespective stationary contacts, and secured thereto as hereinbeforedescribed.

The operation of tap changer 10 requires only that the handle 130 andshaft means 110 be turned until the pointed end 190 of the handle 130 isin the desired tap position. Turning the handle 130 counterclockwise,viewing the tap changer 10 as shown in the position of FIG. 3, until pin136 hits the positive stop provided by one side of projection 140, willcause the tap changer 10 to be in operating tap position No. 1. Turningthe handle and shaft clockwise until pin 136 hits the positive stopprovided by the other side of the projection 140 will cause the tapchanger to be in operating position No. 5. As the handle and shaft areturned, one side of the contact shoe will wipe on one of the stationarycontacts until reaching the small end of its trapezoidal configuration.The small end will continue to wipe across the contact, with theoutwardly extending end of the leaf spring being forced inwardly towardthe shaft means 110. As soon as the last portion of the small end of thecontact shoe has moved over the stationary contact, the contact shoewill snap into the next operating position between two adjacentstationary contacts, under the influence of the bent leaf spring. Oncein the new operating position, the leaf spring will continue to maintaina radial urging of the contact shoe against the stationary contacts, toassure good electrical contact.

FIG. 4 is an elevational view, partially in section, of a tap changer10' constructed according to another embodiment of the invention. Likereference numerals in FIGS. 2 and 4 indicate like components, and likereference numerals, except for a prime mark in FIG. 4, indicate similarbut modified components. The basic difference between the tap changers10 and 10 shown in FIGS. 2 and 4, respectively, is the construction ofthe movable contact assembly, with the construction of the movablecontact assembly shown in FIG. 4 enabling the overall length of the tapchanger 10' to be reduced, compared with the overall length of the tapchanger 10 shown in FIG. 2. Tap changer 10' has also been modified incertain other ways, to be hereinafter described, which modifications maybe used in the construction of the tap changer 10 shown in FIGS. 1 and2, if desired.

More specifically, tap changer 10' shown in FIG. 4, is mounted throughthe side wall portion 12 of an electrical distribution transformer, withits operating mechanism 11' being disposed below the oil level 14 of thetransformer. The insulating base member 20' of tap changer 10',including its stationary contacts, such as stationary contacts 32 and40, is similar to that hereinbefore described, with the base 20 beingturned 180 about its longitudinal axis, compared with its FIGS. 1 and 2orientation, to illustrate its use with a metallic mounting bracket Themounting hub 60', which may be machined or die cast of a suitable metal,such as aluminum or brass, has been changed in this embodiment toreverse the mounting flange, and thus enable the mounting hub 60' to beinserted into an opening in the casing 12 from the outside thereof,prior to its assembly with the operating mechanism 11'. Mounting hub 60has a threaded portion 240 sized to enable it to be inserted through anopening in the casing 12, until a flanged portion 241 contacts thecasing 12. The flanged portion'241 is formed by an outward step fromportion 240 to a portion 242 of larger diameter. The flanged portion 241has an annular groove formed therein which contains a gasket member 244,which hermetically seals the opening in the casing 12 when the mountingnuts 246 are threadably engaged with portion 240 and tightened. Prior tothreading the nuts 246 on the threaded portion 240 of the mounting hub60, portion 94 of the mounting bracket 90' may be inserted over thethreaded portion 240, to secure the mounting bracket to the mounting hub60.

The operating shaft includes a molded insulating portion 200, formed ofa material such as a glass filled polyamide, or a glass filledpolyester, and metallic inserts 202 and 206, formed of a material suchas brass, extend coaxially outward from opposite ends of the moldedinsulating portion of the shaft. Insert 202 includes two spacedcircumferential grooves in which O-rings 117 and 119 are disposed, whichseal the opening through the mounting hub 60' when the insert 202 isinserted therethrough. An opening is provided near the outwardlyextending end 114 of insert 202, for receiving a pin 168 which orientsand secures the operating handle 130 to the operating shaft 110'.

Insert 206 is threaded on its outwardly extending end, to receive a nut224, the purpose of which will be hereinafter explained.

Operating shaft 1 10 also has a radial and thrust bearing 204 moldedtherein, instead of utilizing separate washer and pin members. Retainerwasher 134 may be used, if desired, but it is not essential, as theoperating handle 130 will prevent movement of the shaft 110 in thedirection from its end 114' to its end 112'.

The movable contact assembly has been changed in this embodiment, toenable the axial length of the tap changer switch 10 to be reduced,compared with the tap changer switch 10 of FIGS. 1 and 2. FIG. 5 is anexploded, perspective view of the movable contact assembly 120', whichwill be referred to, along with FIG. 4, in the following description ofthe new contact assembly 120'.

The molded portion 200 of the operating shaft 110' has a circularprojection 208 disposed transverse to the longitudinal metallic housing212 having a substantially U-shaped portion 217, and a flat top portion219 which joins the upwardly extending ends of the U-shaped portion 217.The housing 212 has first and second ends 213 and 215, a major opening218 which extends between its ends, and aligned slots or openings 214and 221 which are disposed through the leg portions of the U-shapedmember 217. The top portion 219 has an integral'tap portion 216 whichextends outwardly therefrom, in

substantially the same shoe 144 is fixed.

The metallic housing 212, with the contact shoe 144 fixed thereto, istelescoped over end 112 of the operating shaft and aligned with theprojection 208, such that spring member 236 presses against the insidesurface of the top portion 219. Thus,

plane, to which the contact or shorting the housing 212 and contact shoe144 are urged radially outward, away from the axis of the operatingshaft 110', by the spring member 236.

A pin 230 is disposed through an opening 210 in the molded portion 200of the operating shaft, such that its ends ride in the slots 214 and 22]disposed in the U-shaped housing 212. A fiat plate member 220 havingfirst and second major opposed sides or surfaces, and an opening 222which extends between its major opposed surfaces, is telescoped over end112 of the operating shaft 110, against the shoulder 23] formed by theend of the molded portion 200, with one of its major surfaces beingagainst the end 213 of the housing 212. Nut 224 is threadably engagedwith the outwardly extending threaded portion of insert 206, and it isadvanced inwardly until it secures the plate member 220 firmly againstshoulder 231. The housing 212 and its contact shoe 144 are now free toslide back and forth without cocking or tipping, as it is guided by oneof the major surfaces of the plate member 220, and by the pin member 230riding in the slots 214 and 221 of the housing 217. When the operatinghandle 130 is turned to actuate the tap changer switch 10' to a newoperating position, the contact shoe 144 and housing 217 will be pushedinwardly, by one of the stationary contacts, towards the axis of theoperating shaft 110' compressing the spring 236 between the housing 212and the operating shaft. As the interfering stationary contact iscleared by the contact shoe, the contact shoe and its associated housing212 will snap outwardly, away from the operating shaft 110, due to theinfluence of the spring member 236, to force the contact shoe 144 firmlybetween and in contact with two stationary contacts, as hereinbeforedescribed relative to FIGS. 1 and 2.

in the assembly of the tap changer switch 10', the operating shaft 110'and its movable contact assembly 120 may be inserted through the openingin the base member The mounting hub 60 and the bracket member 90 maythen be fixed to the casing 12 with the nut members 246. End 114 of theoperating shaft 110' may then be inserted through the opening in themounting hub 60', and secured in position by connecting the base member20' to the mounting bracket 90', and by fixing the operative handle 130to the operating'shaft 110'. Since the movable. contact assembly 120" no-longer requires a relatively. long leaf spring membenthe operatingshaft 110' may be. reduced in length accordingly, which reduces theoverall length of the tap changer switch 10', presentinglessinterference within the transformer casing to theother parts mountedabove the transformer.

FIG. 6 is a fragmentary, elevationalview, partially in section, of a tapchanger switch 10'' constructed according to still another embodiment ofthe invention. Tapchanger 10'" is similar in construction to tap changer10 shown in FIG. 4, except for the movable contact assembly. Instead ofa separate the core and coil assembly of contact housing which movesrelative to the shaft, as disclosed in FIG. 4, FIG. 6 discloses anembodiment of the invention wherein the contact housing ,is fixed totheshaft, and thus it may economically be formed as an integral part ofthe insulating portion of the operating shaft. v

More specifically, tap changer 10' includes an insulating base portion20", constructed as hereinbefore described, and a movable contactassembly 250. Movable contact assembly 250 includes a contact housing256, a helical spring 260, and a roller type contact assembly 262. Thecontact housing 256 may be'formed as an integral portion ofthe operatingshaft 252, with the remaining portion of the operating shaft beingsimilar in construction to the operating shaft shown in FIG. 4. Contacthousing 256, which may be formed of any suitable insulating material,such as a glass filled polyamide, includes first and second spaced,parallel finger" portions 257 and 259, respectively, which defineaslot'26l having an open end and a closed end. A circular projection 258,

disposed with its axis'transverse to the an er operating shaft 252,extends into the slot 261 from its closed end, and the spring 260 isdisposed in the slot 261 such that it encircles the projection 258. a

The movableroller contact assembly 262, which is formed of a goodelectrical conductor, such as brass, has a substantially spool-likeconfiguration, including first and second wafer or disc-shaped contactmembers 264 and 266, which are held in fixed, spaced parallel relationby a coaxially disposed shaft member 268 of smaller diameter than thecontact members.

The movable contact assembly 262 is disposed in the slot 261 such thatthe shaft 268 extends through the slot 261 and the spring 260 exerts anoutward force on the shaft 268. Shaft member 268 has a diameter selectedto allow a smooth, free, sliding fit between the shaft and the innerwalls of the slot 261 with minimal play, and the length of the shaft 268isselected to provide a smooth, free, sliding fit between the innersurfaces of the contact members 264 and 266 and the surfaces of fingers257 and 259 which are perpendicular to the longitudinal axis ofoperating shaft 252, such as surface 269.

In the assembly of tap changer switch l0" the spring 260 is placed overthe projection 258, the shaft portion 268 of the roller contact assembly262'is placed in the slot 261, and pressed inwardly against the spring260; The handle end of the base member 20, and a washer 254 is slippedover the operating shaft, which functions as a first bearing, and alsoto prevent axial movement of the operating shaft, if desired. Axialmovement of the operating shaft in the opposite direction is preventedby projection 271 on the operating shaft, which functions as a secondbearing. vThe assembly of tap changer switch 10 may then be completed,asjhereinbefore described relative to tap changer 10' shown in F 16.4.

In the operation of tap changer 10", when the operating shaft 252 isrotated to select a new tap position, the roller contact assembly 262will be forced inwardly byone ofthe stationary contacts, toward the axisof the operating shaft, and against the outward urging of the spring260} As the centerline of the interfering stationary contact is passed,'roller contact 262 snaps outwardly, under the urging influence of thespring 260,16 force the contact members 264 and'266 of the contactassembly 262 into firm engagement with two adjacent stationary'contacts.H v

lrisur'nrnary, there has been disclosed a new and improved tap changeradapted for mounting within the casing of an electricaldistributiontypetransformenwhich is operable from outside the casing.The operating shaft the gtap jchangcr extends outwardly from both sidesof an insulating base assembly which carries the stationary contact,members, .toiotatably support the shaft intermediate its ends as wellas-at amounting hub fixed to the casing of the transformer. Thestationary contacts extend outwardly from one side of the insulatingbase member, away from the casing wall, and the movable contact memberis mounted on the shaft on this same side of the insuother apparatusmounted above the core-winding assembly.

I claim as my invention: 1. A tap changer switch adapted for mountingwithin the casing of an electrical distribution transformer, andoperable from outside the casing, comprising:

an insulating base member having first and second sides,

and an opening which extends therebetween,

a plurality of stationary electrical contact members, said stationaryelectrical contact members being carried by said insulating base membersuch that they extend outwardly from its first side, in spaced parallelrelation with one another about the opening in said insulating basemember,

a mounting hub having first and second ends, a mounting flangeintermediate its ends, and an opening extending between its ends,

means holding said insulating base member and said mounting hub inspaced relation, with their openings in coaxial alignment,

shaft means having first and second ends, disposed through the openingin said insulating base member, with its first and second ends extendingoutwardly from the first and second sides, respectively, of saidinsulating base member, and with its second end also extending throughthe opening in said mounting hub, and beyond the second end of themounting hub by a predetermined dimension, said shaft means being asingle member formed of electrical insulating material,

means rotatably supporting said shaft means in said insulating basemember,

a movable contact assembly including a contact, and means urging thecontact outwardly against two adjacent stationary contact members,

and handle means fixed to the second end of said shaft means forrotating said shaft means and selectively engaging the contact with thedesired stationary electrical contact members.

2. A tap changer switch adapted for mounting within the casing of anelectrical distribution transformer, and operable from outside thecasing, comprising:

an insulating base member having first and second sides,

and an opening which extends therebetween,

a plurality of stationary electrical contact members, said stationaryelectrical contact members being carried by said insulating base membersuch that they extend outwardly from its first side, in spaced parallelrelation with one another about the opening in said insulating basemember,

a mounting hub having first and second ends, a mounting flangeintermediate its ends, and an opening extending between its ends,

means holding said insulating base member and said mounting hub inspaced relation, with their openings in coaxial alignment,

shaft means having first and second ends, disposed through the openingin said insulating base member, with its first and second ends extendingoutwardly from the first and second sides, respectively, of saidinsulating base member, and with its second end also extending throughthe opening in said mounting hub, and beyond the second end of themounting hub by a predetermined dimension,

means rotatably supporting said shaft means in said insulating basemember,

a movable contact assembly including a contact, and means urging thecontact outwardly against two adjacent stationary contact members,

said means including a leaf spring having first and second ends, withthe contact being fixed to its first end, and with its second end beingfixed to the shaft means, adjacent to the first end thereof,

and handle means fixed to the second end of said shaft means forrotating said shaft means and selectively engaging the contact with thedesired stationary electrical contact members.

3. The tap changer switch of claim 2 wherein said shaft means includesconnected portions formed of electrical insulating material and metal,with the leaf spring being fixed to an insulating portion.

4. A tap changer switch adapted for mounting within the casing of anelectrical distribution transformer, and operable from outside thecasing, comprising:

an insulating base member having first and second sides,

and an opening which extends therebetween,

a plurality of stationary electrical contact members, said stationaryelectrical contact members being carried by said insulating base membersuch that they extend outwardly from its first side, in spaced parallelrelation with one another about the opening in said insulating basemember,

a mounting hub having first and second ends, a mounting flangeintermediate its ends, and an opening extending between its ends,

means holding said insulating base member and said mounting hub inspaced relation, with their openings in coaxial alignment,

shaft means having first and second ends, disposed through the openingin said insulating base member, with its first and second ends extendingoutwardly from the first and second sides, respectively, of saidinsulating base member, and with its second end also extending throughthe opening in said mounting hub, and beyond the second end of themounting hub by a predetermined dimension,

means rotatably supporting said shaft means in said insulating basemember,

a movable contact assembly including a contact, and means urging thecontact outwardly against two adjacent stationary contact members,

said movable contact assembly including a housing disposed about theshaft means to which the contact is fixed, and the means which urges thecontact against the stationary contact members includes spring meansdisposed between a portion of the housing and the shaft means,

means guiding said housing through a predetermined movement transverseto the axis of the shaft means, against the urging of said spring means,when the shaft means is actuated to change the operating position of thetap changer switch, and handle means fixed to the second end of saidshaft means for rotating said shaft means and selectively engaging thecontact with the desired stationary electrical contact members.

5. The tap changer switch of claim 4 wherein the housing -has anoutwardly extending tab member, to which the contact 6. The tap changerswitch of claim 4 wherein the shaft means has a substantially circularprojection transverse to the axis of the shaft means, about which thespring means is disposed.

7. The tap changer switch of claim 4 wherein the means which guides thehousing through the predetermined movement transverse to the axis of theshaft means includes first and second slots disposed in opposite sidesof the housing, a pin member disposed through the shaft, means such thatits ends ride in the first and second slots, and a flat plate memberfixed to the shaft with its major surfaces perpendicular to the axisthereof, with one of its major surfaces being aligned with and insliding contact with an end of the metallic housing.

8. A tap changer switch adapted for mounting within the casing of anelectrical distribution transformer, and operable from outside thecasing, comprising:

an insulating base member having first and second sides,

and an opening which extends therebetween,

a plurality of stationary electrical contact members, said stationaryelectrical contact members being carried by said insulating base membersuch that they extend outwardly from its first side, in spaced parallelrelation with one another about the opening in said insulating basemember,

a mounting hub having first and second ends, a mounting flangeintermediate its ends, and an opening extending between its ends,

means holding said insulating base member and said mounting hub inspaced relation, with their openings in coaxial alignment,

shaft means having first and second ends, disposed through the openingin said insulating base member, with its first and second ends extendingoutwardly from the first and second sides, respectively, of saidinsulating base member, and with its second end also extending throughthe opening in said mounting hub, and beyond the second end of themounting hub by a predetermined dimension,

means rotatably supporting said shaft means in said insulating basemember,

a movable contact assembly including a contact, and means urging thecontact outwardly against two adjacent stationary contact members,

and handle means fixed to the second end of said shaft means forrotating said shaft means and selectively engaging the contact with thedesired stationary electrical contact members, the first end of saidshaft means including a contact housing fixed thereto, with said contacthousing having first and second spaced finger portions which define aslot having an open end and a closed end, and a projection disposedtransverse to the axis of the shaft means which extends into the slotfrom its closed end, said means which urges the contact against thestationary contact members including spring means disposed about theprojection, with the contact riding in the slot,

9. The tap changer switch of claim 8 wherein the contact is asubstantially spool-shaped roller contact having first and second spacedcircular members joined by a shaft, said shaft being sized to ride inthe slot defined by the spaced finger portions of the contact housing.

10. The tap changer switch of claim 8 wherein the contact housing is anintegral part of the shaft means.

1. A tap changer switch adapted for mounting within the casing of anelectrical distribution transformer, and operable from outside thecasing, comprising: an insulating base member having first and secondsides, and an opening which extends therebetween, a plurality ofstationary electrical contact members, said stationary electricalcontact members being carried by said insulating base member such thatthey extend outwardly from its first side, in spaced parallel relationwith one another about the opening in said insulating base member, amounting hub having first and second ends, a mounting flangeintermediate its ends, and an opening extending between its ends, meansholding said insulating base member and said mounting hub in spacedrelation, with their openings in coaxial alignment, shaft means havingfirst and second ends, disposed through the opening in said insulatingbase member, with its first and second ends extending outwardly from thefirst and second sides, respectively, of said insulating base member,and with its second end also extending through the opening in saidmounting hub, and beyond the second end of the mounting hub by apredetermined dimension, said shaft means being a single member formedof electrical insulating material, means rotatably supporting said shaftmeans in said insulating base member, a movable contact assemblyincluding a contact, and means urging the contact outwardly against twoadjacent stationary contact members, and handle means fixed to thesecond end of said shaft means for rotating said shaft means andselectively engaging the contact with the desired stationary electricalcontact members.
 2. A tap changer switch adapted for mounting within thecasing of an electrical distribution transformer, and operable fromoutside the casing, comprising: an insulating base member having firstand second sides, and an opening which extends therebetween, a pluralityof stationary electrical contact members, said stationary electricalcontact members being carried by said insulating base member such thatthey extend outwardly from its first side, in spaced parallel relationwith one another about the opening in said insulating base member, amounting hub having first and second ends, a mounting flangeintermediate its ends, and an opening extending between its ends, meansholding said insulating base member and said mounting hub in spacedrelation, with their openings in coaxial alignment, shaft means havingfirst and second ends, disposed through the opening in said insulatingbase member, with its first and second ends extending outwardly from thefirst and second sides, respectively, of said insulating base member,and with its second end also extending through the opening in saidmounting hub, and beyond the second end of the mounting hub by apredetermined dimension, means rotatably supporting said shaft means insaid insulating base member, a movable contact assembly including acontact, and means urging the contact outwardly against two adjacentstationary contact members, said means including a leaf spring havingfirst and second ends, with the contact being fixed to its first end,and with its second end being fixed to the shaft means, adjacent to thefirst end thereof, and handle means fixed to the second end of saidshaft means for rotating said shaft means and selectively engaging thecontact with the desired stationary electrical contact members.
 3. Thetap changer switch of claim 2 wherein said shaft means includesconnected portions formed of electrical insulating mAterial and metal,with the leaf spring being fixed to an insulating portion.
 4. A tapchanger switch adapted for mounting within the casing of an electricaldistribution transformer, and operable from outside the casing,comprising: an insulating base member having first and second sides, andan opening which extends therebetween, a plurality of stationaryelectrical contact members, said stationary electrical contact membersbeing carried by said insulating base member such that they extendoutwardly from its first side, in spaced parallel relation with oneanother about the opening in said insulating base member, a mounting hubhaving first and second ends, a mounting flange intermediate its ends,and an opening extending between its ends, means holding said insulatingbase member and said mounting hub in spaced relation, with theiropenings in coaxial alignment, shaft means having first and second ends,disposed through the opening in said insulating base member, with itsfirst and second ends extending outwardly from the first and secondsides, respectively, of said insulating base member, and with its secondend also extending through the opening in said mounting hub, and beyondthe second end of the mounting hub by a predetermined dimension, meansrotatably supporting said shaft means in said insulating base member, amovable contact assembly including a contact, and means urging thecontact outwardly against two adjacent stationary contact members, saidmovable contact assembly including a housing disposed about the shaftmeans to which the contact is fixed, and the means which urges thecontact against the stationary contact members includes spring meansdisposed between a portion of the housing and the shaft means, meansguiding said housing through a predetermined movement transverse to theaxis of the shaft means, against the urging of said spring means, whenthe shaft means is actuated to change the operating position of the tapchanger switch, and handle means fixed to the second end of said shaftmeans for rotating said shaft means and selectively engaging the contactwith the desired stationary electrical contact members.
 5. The tapchanger switch of claim 4 wherein the housing has an outwardly extendingtab member, to which the contact is fixed.
 6. The tap changer switch ofclaim 4 wherein the shaft means has a substantially circular projectiontransverse to the axis of the shaft means, about which the spring meansis disposed.
 7. The tap changer switch of claim 4 wherein the meanswhich guides the housing through the predetermined movement transverseto the axis of the shaft means includes first and second slots disposedin opposite sides of the housing, a pin member disposed through theshaft means such that its ends ride in the first and second slots, and aflat plate member fixed to the shaft with its major surfacesperpendicular to the axis thereof, with one of its major surfaces beingaligned with and in sliding contact with an end of the metallic housing.8. A tap changer switch adapted for mounting within the casing of anelectrical distribution transformer, and operable from outside thecasing, comprising: an insulating base member having first and secondsides, and an opening which extends therebetween, a plurality ofstationary electrical contact members, said stationary electricalcontact members being carried by said insulating base member such thatthey extend outwardly from its first side, in spaced parallel relationwith one another about the opening in said insulating base member, amounting hub having first and second ends, a mounting flangeintermediate its ends, and an opening extending between its ends, meansholding said insulating base member and said mounting hub in spacedrelation, with their openings in coaxial alignment, shaft means havingfirst and second ends, disposed through the opening in said insulatingbase member, with its first and Second ends extending outwardly from thefirst and second sides, respectively, of said insulating base member,and with its second end also extending through the opening in saidmounting hub, and beyond the second end of the mounting hub by apredetermined dimension, means rotatably supporting said shaft means insaid insulating base member, a movable contact assembly including acontact, and means urging the contact outwardly against two adjacentstationary contact members, and handle means fixed to the second end ofsaid shaft means for rotating said shaft means and selectively engagingthe contact with the desired stationary electrical contact members, thefirst end of said shaft means including a contact housing fixed thereto,with said contact housing having first and second spaced finger portionswhich define a slot having an open end and a closed end, and aprojection disposed transverse to the axis of the shaft means whichextends into the slot from its closed end, said means which urges thecontact against the stationary contact members including spring meansdisposed about the projection, with the contact riding in the slot. 9.The tap changer switch of claim 8 wherein the contact is a substantiallyspool-shaped roller contact having first and second spaced circularmembers joined by a shaft, said shaft being sized to ride in the slotdefined by the spaced finger portions of the contact housing.
 10. Thetap changer switch of claim 8 wherein the contact housing is an integralpart of the shaft means.